Heretofore, filter beds for removing dispersed oils from oil-in-water emulsions utilized a sand or anthracite granular medium to trap the oil in the interstices of the medium.
Recent reasearch, however, has shown that a more effective filtering mechanism would allow the oil to wet and adhere to the medium material in an adsorptive manner. Conventional sand or anthracite materials do not normally have adsorptive characteristics, and their ability to remove and retain oils is therefore limited.
After extensive screening of various sand and glass materials for filter bed use, a chemical treatment was developed to enhance the affinity of sand for the oils dispersed in the water. The chemical treatment consisted of treating a 16 to 20 mesh sand with a primary aliphatic amine, as illustrated in U.S. Pat. No. 3,901,818 issued Aug. 26, 1975. A filter bed of this treated sand was shown to have superior oil removal ability, but failed to retain this ability after an extended filtering run. After backwashing, this bed of aliphatic amine-treated sand did not regain its former ability to remove the entrained oils.
The present invention has developed new and improved chemically treated filter media for removing oil from oil-water emulsions, which media will regain its ability to remove the oils even after many backwashings.
The invention uses a chemical treatment which creates a siloxane bond between a lipophilic hydrocarbon and a granulated sand or glass substrate. This chemical treatment binds the lipophilic hydrocarbon to the surface of the medium where it is exposed to the flowing oil-water stream.
A similar chemical treatment is shown and described in U.S. Pat. No. 4,017,528, issued Apr. 12, 1977. The above patent teaches the creation of a siloxane-type bond in porous silicon dioxide substrates to improve their absorptive properties for chromatography purposes.
The present invention desires to improve the adsorptive properties of a silicon dioxide granulated substrate, but requries that the substrate be one which is non-porous rather than porous.
In another sense, the above treatment when applied to granular substrates for purposes of this invention, will not provide a workable filter medium. This is so, because the resulting adsorptivity of the filter bed will cause the granular particles to agglomerate. This results in a plugging or general fouling of the bed such that it will not filter properly. To correct this, it has been discovered that treated granular glass material can be mixed in substantially equal proportions with non-treated glass materials in order to provide uniform flow paths through the bed cross-section.
Also, it is contemplated that glass granules may be only partially treated with alkoxy silanes in order to provide a free flowing filter bed during backwash.
Still another procedure which has been found to provide an efficacious filter bed is to fully treat "filter sand" with an alkoxy silane. The filter sand having a less adsorptive character than the glass granules is susceptible to a full chemical treatment without producing an overly oil-wettable filter bed.
The three aforementioned procedures will provide filter media which not only have superior oil-wetting properties, but which also effectively regain their oil-wettability even after many backwashes.